Can a present or future event bring about a past event? An answer to this question is demanded by many other interesting questions. Can anybody, even a god, do anything about what has already occurred? Should we plan for the past, as well as for the future? Can anybody precognise the future in a way quite different from normal prediction? Do the causal laws and the past jointly preclude free action? Does current physical theory entail a consistent version of backwards causation? Recent articles on the problem of backwards causation have drawn attention to the importance of the principle of the fixity of the past: that the past is now fixed. It can be shown that the standard argument against backwards causation (the bilking experiment) simply builds in the assumption of past fixity. A fixed past deprives future events of past efficacy. This has naturally led to the speculation that by abandoning past fixity real power over the past may be possible.In this paper I show that in order to have an interesting thesis of backwards causation it is not enough simply to drop past fixity. More must go. In particular, to ensure what could be called future-to-past efficacy we must abandon two entrenched principles of permanence: the principle of permanent fixity, and the principle of permanent truth. The only alternative for backwards causal theorists is to embrace real contradictions in nature.